hydroelectric power plant

1. Power Plant

2. CLASSIFICATION OF POWER PLANT
CYCLE
Power plants cycle generally divided in to the following groups,
1 Vapour Power Cycle
(Carnot cycle, Rankine cycle, Regenerative cycle, Reheat cycle, Binary vapour
cycle)
2 Gas Power Cycles
(Otto cycle, Diesel cycle, Dual combustion cycle, Gas turbine cycle.)

3. 1. CARNOT CYCLE
• The Carnot Cycle has been described as being the most efficient
thermal cycle possible, wherein there are no heat losses, and
consists of four reversible processes, two isothermal and two
adiabatic.
• It has also been described as a cycle of expansion and compression
of a reversible heat engine that works with no loss of heat.
• By using the second law of thermodynamics it is possible to show
that no heat in the engine can be more efficient than a reversible
heat engine working between two fixed temperature limits.
• This heat engine is known as the Carnot cycle and consists of the
following processes

4. This cycle is of great value to heat power theory although it
has not been possible to construct a practical plant on this
cycle.
It has high thermodynamics efficiency.
It is a standard of comparison for all other cycles.
The thermal efficiency (η ) of Carnot cycle is as follows:
η = (T1
- T2
)/T1
where, T1
= Temperature of heat source, T2 =
Temperature of receiver

5. • 1 to 2 isentropic expansions
• 2 to 3 Isothermal heat rejection
• 3 to 4 isentropic compression
• 4 to 1 Isothermal heat supply

6. Rankine cycle
• The Rankine cycle is an ideal thermodynamic cycle involving a constant
pressure heat engine which converts heat into mechanical work. The heat
is supplied externally in this cycle in a closed loop, which uses either water
or any other organic fluids as a working fluid.
• The Rankine cycle is a theoretical cycle on which the power plants work.
This cycle, which is the basic principle of Steam turbines, is also known as
a modified Carnot cycle. The Carnot cycle is a thermodynamic cycle that
has maximum efficiency.
• Steam engine and steam turbines in which steam is used as working
medium follow Rankine cycle.
• The drawbacks of the Carnot engine like its difficulty to operate practically
or to work with superheated steam are overcome by this cycle.

8. Efficiency of Rankine Cycle = (H1
- H2
)/ (H1
- Hw2
)
where,
H1 = Total heat of steam at entry pressure
H2 = Total heat of steam at condenser pressure (exhaust
pressure)
Hw2= Total heat of water at exhaust pressure

9. In this cycle steam is extracted from a suitable point in the turbine and
reheated generally to the original temperature by flue gases. Reheating
is generally used when the pressure is high say above 100 kg/cm2
. The
various advantages of reheating are as follows:
(i) It increases dryness fraction of steam at ex-haust so that blade erosion
due to impact of water particles is reduced.
(ii) It increases thermal efficiency.
(iii) It increases the work done per kg of steam and this results in reduced
size of boiler.
3 REHEAT CYCLE

10. The disadvantages of reheating are as
follows:
(i) Cost of plant is increased due to
the reheater and its long connections.
(ii) It increases condenser capacity
due to in-creased dryness fraction.
Fig. 1.4 shows flow diagram of reheat cycle.
First turbine is high-pressure turbine and
second turbine is low pressure (L.P.) turbine.
This cycle is shown on T-S (Temperature
entropy) diagram (Fig. 1.5).

11. If,
H1 = Total heat of steam at 1
H2
= Total heat of steam at 2
H3
= Total heat of steam at 3
H4
= Total heat of steam at 4
Hw4
= Total heat of steam at 4
Efficiency = {(H1
- H2
) + (H3
- H4
)}/{H1
+ (H3
- H2
) - Hw4
}

12. 4 REGENERATIVE CYCLE (FEED WATER
HEATING)
• The process of extracting
steam from the turbine at
certain points during its
expansion and using this
steam for heating for feed
water is known as
Regeneration or Bleeding of
steam. The arrangement of
bleeding the steam at two
stages is shown in Fig. 1.6.

13. m2
= Weight of bled steam at a per kg of feed water heated m2
= Weight of bled steam at a per
kg of feed water heated H1
= Enthalpies of steam and water in boiler
Hw1
= Enthalpies of steam and water in boiler H2
, H3
= Enthalpies of steam at points a and b
t2
, t3
= Temperatures of steam at points a and b
H4
, Hw4
= Enthalpy of steam and water exhausted to hot well. Work done in turbine per kg of
feed water between entrance and a
= H1
- H2
Work done between a and b = (1 - m2
)(H2
- H3
)
Work done between b and exhaust = (1 - m2
- m3
)(H3
- H4
) Total heat supplied per kg of feed
water = H1
- Hw2
Efficiency (η ) = Total work done/Total heat supplied
{(H1
- H2
) + (1 - m2
)(H2
-H3
) + (1 - m2
- m3
)(H3
- H4
)}/(H1
- Hw2
)

14. 5 BINARY VAPOUR CYCLE
In this cycle two working fluids are
used. Fig. 1.7 shows Elements of Binary
vapour power plant. The mercury boiler
heats the mercury into mercury vapours
in a dry and saturated state.
These mercury vapours expand in the
mercury turbine and then flow through
heat exchanger where they transfer the
heat to the feed water, convert it into
steam. The steam is passed through the
steam super heater where the steam is
super-heated by the hot flue gases. The
steam then expands in the steam
turbine.

15. 6 REHEAT-REGENERATIVE CYCLE
In steam power plants using high steam pressure
reheat regenerative cycle is used.
The thermal efficiency of this cycle is higher than
only re-heat or regenerative cycle.
Fig. 1.8 shows the flow diagram of reheat
regenerative cycle.
This cycle is commonly used to produce high
pressure steam (90 kg/cm2
) to increase the cycle
efficiency.

16. FORMULA SUMMARY
Rankine efficiency
(H1
- H2
)/(H1
- Hw2
)
Efficiency ratio or Relative efficiency
Indicated or Brake thermal efficiency/Rankine efficiency
Thermal efficiency = 3600/m(H1
- Hw2
), m = steam flow/kw
hr
Carnot efficiency = (T1
- T2
)/T1

18. • A typical Rankine cycle has four thermodynamic processes which are explained below referring to
all the diagrams. Let us assume that the cycle is operating at temperatures ranging from 0 °C to
400 °C.
• Process 1-2: The working fluid (saturated liquid) entering the pump, is pumped from a low to high
pressure. This is also known as isentropic compression. The input energy is needed at this stage.
• Process 2-3: Liquid at a high pressure entering the boiler is heated by an external heat source at a
constant pressure. The liquid is converted to dry saturated steam by constant pressure heat
addition in the boiler.
• Process 3-4: The dry saturated steam from the boiler expands as it enters the turbine. It is also
known as isentropic expansion. Due to this, the temperature and pressure of the steam decrease.
• Process 4-1: The wet vapour entering the condenser at this stage is condensed at a constant
pressure. It is then converted to saturated liquid. This process is also known as constant pressure
heat rejection in the condenser.This saturated liquid is again circulated back to the pump, and the
cycle continues. The heat rejected or the exhaust heat after the final stage is represented as
(Q_{out}).

20. Efficiency of Rankine Cycle
Let us consider these terms that are essential to calculate the efficiency of the cycle.
Q = Rate of heat flow in the system (towards or away)
(WT) = Mechanical work done by the turbine
(WP)= Mechanical work done by the pump
(h1),(h2),(h3),and(h4)= Specific enthalpies of water at states 1, 2, 3, and 4 respectively referring to the T-s diagram in figure 2.
(hf)= Specific enthalpy of water = h (In this cycle)
Applying steady flow energy equation (SFEE) to pump, boiler, turbine, and condenser,
(1) For Pump: (h2+WP=h1⟹WP=h2−h1)
(2) For Boiler: (h2+Qin=h3⟹Qin=h3−h2)
(3) For Turbine: (h3=WT+h4⟹WT=h3−h4)
(4) For Condenser:(h4=Qout+h1⟹Qout=h4−h1)
Now, the Rankine cycle efficiency with pump is given as,
Rankine=WnetQin=WT−WPQin
= (frac(h3−h4) (
− h2−h1)(h3−h2)).
Similarly, the Rankine cycle efficiency without pump work is given as,
(ηRankine=1−QoutQin=1−(h4−h1)(h3−h2))
In real applications, the calculation of this efficiency falls below the ideal efficiency of the Rankine cycle. Let us see how the real cycle
differs from the ideal cycle.

21. • There are three types of hydropower facilities:
impoundment, diversion, and pumped storage. Some
hydropower plants use dams and some do not.
• Although not all dams were built for hydropower, they have
proven useful for pumping tons of renewable energy to the
grid.
• Hydropower plants range in size from small systems
suitable for a single home or village to large projects
producing electricity for utilities.

22. Impoundment
• The most common type of hydroelectric power plant is an
impoundment facility. An impoundment facility, typically a
large hydropower system, uses a dam to store river water in
a reservoir. Water released from the reservoir flows through
a turbine, spinning it, which in turn activates a generator to
produce electricity. The water may be released to meet
changing electricity needs or other needs, such as flood
control, recreation, fish passage, and other environmental
and water quality needs

24. diversion
• A diversion, sometimes called a “run-of-river” facility,
channels a portion of a river through a canal and/or a
penstock to utilize the natural decline of the river bed
elevation to produce energy. A penstock is a closed conduit
that channels the flow of water to turbines with water flow
regulated by gates, valves, and turbines. A diversion may
not require the use of a dam.

26. pumped storage
• Another type of hydropower, called pumped storage hydropower, or
PSH, works like a giant battery. A PSH facility is able to store the
electricity generated by other power sources, like solar, wind, and
nuclear, for later use. These facilities store energy by pumping water
from a reservoir at a lower elevation to a reservoir at a higher
elevation.
• When the demand for electricity is low, a PSH facility stores energy by
pumping water from the lower reservoir to an upper reservoir. During
periods of high electrical demand, the water is released back to the
lower reservoir and turns a turbine, generating electricity.

28. Sizes Of Hydroelectric Power Plants
• Hydropower facilities range in size from large power plants, which supply many
consumers with electricity, to small and even ‘micro’ plants, which are operated by
individuals for their own energy needs or to sell power to utilities.
• Large Hydropower
• Although definitions vary, DOE defines large hydropower plants as facilities that
have a capacity of more than 30 megawatts (MW).
• Small Hydropower
• Although definitions vary, DOE defines small hydropower plants as projects that
generate between 100 kilowatts and 10 MW.
• Micro Hydropower
• A micro hydropower plant has a capacity of up to 100 kilowatts. A small or micro
hydroelectric power system can produce enough electricity for a single home,
farm, ranch, or village.